The present invention relates to a thermal master making device for making a master out of a thermosensitive stencil with a thermal head. More particularly, the present invention is concerned with a thermal master making device capable of stably perforating a stencil at a high speed and extending the life of heating elements included in a thermal head.
A thermal master making device is included in, e.g. a thermal stencil printer. Various technologies including one for obviating so-called offset have been proposed for a thermal master making device. The technology for obviating offset is taught in, e.g., Japanese Patent Laid-Open Publication No. 2-67133 corresponding to Japanese Patent No. 2,732,532. Also, Japanese Patent Laid-Open Publication No. 8-67061, for example, discloses a technology using a thermal head similar in configuration to a thermal head included in the present invention, and controlling the diameter of perforations to be formed in a thermoplastic resin film included in a stencil in such a manner as to form an optimal image. Further, Japanese Patent Laid-Open Publication No. 8-132584 proposes a technology for reducing a master making time.
However, the above conventional technologies have some problems left unsolved, as follows. Neither Laid-Open Publication No. 2-67133 nor Laid-Open Publication No. 8-67061 gives consideration to the increasing demand for the reduction of a master making time. Moreover, Laid-Open Publication No. 8-67061 basically proposes the configuration of a heating element for making resolution in the subscanning direction variable and is therefore different in object from the present invention. Although Laid-Open Publication No. 8-132584 is directed toward a short master making time, it cannot implement the further reduction of a master making time required of advanced master making devices.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 4-163159, 6-320851, 7-52515, 7-241974 and 8-132723, U.S. Pat. Nos. 5,689,297, 5,685,222 and 5,809,879, and pending U.S. patent application Ser. No. 08/986,636 field Dec. 8, 1997.